Embodiments of the invention relate to sensor communications for railways, and, more particularly, to train approach annunciators for rail systems and level crossing protection systems.
Operators of railway networks, for example the Deutsche Bahn A G, generally use train-controlled or signal-controlled level crossing protection systems, e.g., a barrier or crossing gate for road traffic, or a combination of both. These level crossing protection systems may have different security levels, for example US and Fu systems for train-controlled systems and Hp systems for signal-controlled systems. The term “level crossing” (also called a railroad crossing, road through railroad, railway crossing, train crossing, or grade crossing) refers to a crossing on one level (at-grade intersection)—without recourse to a bridge or tunnel—of a railway line by a road, path, or another railroad.
For example, European Patent Application EP 1 187 750 A1 discloses a level crossing protection system having switch parts for controlling at least the road traffic, and a track mounted sensor arrangement for detecting rail vehicles traveling past and at least indirectly controlling the switch parts. The system also includes a decentralized power supply device for operating the sensor arrangement for switching on the railway crossing safety system and a radio link from these sensor arrangements to the railway crossing. This level crossing protection system may only be used where no more than eighty trains per day are passing.
If main signals are available for a track of a railway, the main signals are used to protect the level crossing. An activation and deactivation of the level crossing protection system is effected in the Hp monitoring mode from an interlocking. (An interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings.) The activation occurs automatically from the road logic system. To achieve a timely closure (especially in systems using half barriers, but also when full-barriers are used), electric approach annunciators are desired, to avoid excessive and possibly inappropriate closure times for the road traffic. Similar devices are used in other parts of railways, for example in rail yards, to detect the presence of vehicles and relay information concerning vehicle approach to equipment further down the railway line.
Generally, an approach annunciation is realized with a vehicle sensor in or near the track and with a cable connecting the vehicle sensor to an interlocking, or to a level crossing and from the level crossing to the interlocking. The vehicle sensor recognizes a passing of a train in the direction of a level crossing protection system, and a notification signal is generated and transmitted to the interlocking. In the interlocking, the received notification signal is processed. If the vehicle sensor (or other sensing device or element) is close to the theoretical approach annunciator point, the notification signal may be used directly for the approach annunciation. The theoretical approach annunciator point is the distance from the level crossing where, if a train is detected and a notification signal immediately generated and transmitted to an interlocking, there would be sufficient time to activate a level crossing protection system (barrier, light signal, or signal installation at the level crossing) before arrival of the train, at an expected maximum speed of the train, and without activating the level crossing protection system too far in advance of the train's arrival to pose an inconvenience for those crossing the railway at the level crossing. The theoretical approach annunciator point may be calculated based on the expected maximum speed of the train (e.g. speed limit), the time required to activate the level crossing system, the time delay to generate, transmit, receive, and process a notification signal (assumed to be a short time), and a safety margin (typically, it is desired for the level crossing protection system to be fully activated in advance of the train arriving at the level crossing). In the case that the location of the vehicle sensor or other sensor or sensing element in not optimal, this may be optimized by a delay device for simulating an optimal approach annunciation point that is then used for the calculation of the time of the passage of the train at the level crossing protection system. In both cases, cable conductors to the interlocking or a neighboring interlocking must be available for transmitting the approach annunciation of the train. In this case, a detector or a sensor (rail switch, induction loop, or axle counter) and a cable connection to the interlocking is or are required. If no free conductors are available, a new cable must be installed with all the costly works and accompanying activities of construction work for laying cable.
In particular, in the case of an increasing distance between the approach annunciation point and the level crossing, a conventional wire bound solution is costly and lacks flexibility to quickly adapt to changing requirements. Usually, the necessary cable routing and civil engineer work require lengthy planning and approval processes before the construction work can start. The costs of construction work can only be roughly estimated prior to the actual construction, meaning that an additional budget is required in most cases.